Modeling Guidance and Examples for
Commonly Asked Questions
(Part II)
Reece Parker and Justin Cherry, P.E.
Air Permits Division
Texas Commission on Environmental Quality
Advanced Air Permitting Seminar 2014
What Is Ozone?
• Stratospheric Ozone
O2
sunlight
O + O2
O+O
O3
• Ground-level Ozone
VOC + NOx
Good
sunlight
Bad
O3 (and other products)
Ground-level Ozone Is:
• The main component of smog.
• Not emitted directly in the air but forms when emissions of
precursors, including NOx and VOCs “cook” in the sun:
– Emissions from industrial facilities, electric utilities, motor vehicle exhaust,
gasoline vapors, and chemical solvents are the major man-made sources of
NOx and VOCs.
• Mainly a summertime pollutant because sunlight and hot
weather accelerate its formation.
Ozone levels can be high in both urban and rural areas, often due to
transport of emissions of ozone precursors.
2008 Ground-level Ozone
Standards
• Primary and secondary
8-hr ozone standards:
75 ppb*
*based on the 3-yr average of the
annual fourth highest daily maximum
8-hr ozone concentration
Type of Application
NonAttainment
Review?
PSD Increment:
PSD
Review?
Non-attainment vs. Attainment
Non-attainment Review
Ozone Impact Analysis not required.
Emissions offsets to
improve air quality
PSD Review
An ozone impacts analysis is required when a
project emits:
 100 tpy or more of VOCs
and/or
 100 tpy or more of NOx
Ozone Impacts Analysis
•
Obtain representative monitoring data
•
Determine whether the project area is VOC-limited or
NOx-limited*
•
Quantitative demonstration
•
Qualitative demonstration
*Based on TCEQ’s own SIP photochemical modeling, most of the urban
and rural areas of Texas are NOx-limited.
Quantitative Demonstration
• Photochemical modeling:
 Comprehensive Air Quality Model with extensions
(CAMx)
• Screening approach using AERMOD:
 Demonstration based on comments by EPA for NOxlimited areas
Quantitative Demonstration (Cont.)
• Screening approach using AERMOD:
 Conservative analysis based on NOx modeling:
– Determine if the project is NOx-limited or VOC-limited
– If VOC-limited, determine GLCmax at a distance of 10-11 km
– Assume 90% conversion of NOx to NO2
– Assume 3 ozone molecules per NOx molecule
– Add result to the representative monitored concentration
– Compare to the standard
Example of Quantitative Demonstration
Determine a representative monitor concentration
Project Location
Example (Cont.)
Determine a representative monitor concentration
Monitor Location
3-yr avg of 4th highest
daily maximum 8-hr conc.
69 ppb
Example (Cont.)
Determine GLCmax 10-11 km
from project sources
Example (Cont.)
Model Output
Converting model result to ppb:
2.96 µg/m3 x (100 ppb)/(188 µg/m3) = 1.57 ppb
Example (Cont.)
• Assume 90% conversion of NOX to NO2:
1.57 ppb x 0.9 = 1.413 ppb
• Assume 3 molecules ozone per molecule NOX:
3 x 1.413 ppb = 4.24 ppb
• Add result to monitored concentration:
69 ppb + 4.24 ppb = 73.24 ppb
• Compare to standard:
73.24 ppb < 75 ppb
Qualitative Demonstration
• Assessment of current air quality:
– Ozone trends
– NOX trends
– VOC trends
• Analysis of the project’s potential ozone impact – Selection of
Existing Photochemical Modeling Analyses:
– Modeling simulation (Did photochemical modeling follow EPA
guidance?)
– Source characterization
– Meteorological parameters and regional transport
Example Qualitative Demonstration
Ozone Trends BPA Area
BPA Area Ozone Design Values for all Monitoring Sites (1992-2013)
0.105
8-hr Ozone Design Value (ppm)
0.100
0.095
0.090
0.085
0.080
0.075
0.070
0.065
0.060
Site ID: 482450009
Site ID: 482450101
Site ID: 482451035
1997 8-hr Ozone NAAQS
2008 NAAQS Threshold
Site ID: 482450011
Site ID: 482450102
Site ID: 483611001
2008 8-hr Ozone NAAQS
Site ID: 482450022
Site ID: 482450628
Site ID: 483611100
1997 NAAQS Threshold
Example (Cont.)
NOx Trends (BPA Area)
Summary of NOx Emissions Data in BPA Area (tons per day)
250
200
NOx Emissions (tons per day)
150
100
Nonroad
Nonroad
Nonroad
Onroad
Area
Onroad
Onroad
Area
Area
Point
Point
2008 NEI
2011 NEI
50
Point
0
2005 NEI
Point
Area
Onroad
Nonroad
Example (Cont.)
NOx Trends (BPA Area)
Maximum BPA Area Annual Average NOX Concentration (1998-2013)
16.0
14.0
Annual NOx Concentration (ppb)
12.0
10.0
8.0
6.0
4.0
2.0
0.0
Example (Cont.)
VOC Trends (BPA Area)
Summary of VOC Point and Area Emissions Data in BPA Area (tons per day)
Example (Cont.)
VOC Trends (BPA Area)
Annual Average Level of Ethylene Measured in the BPA Area (1997-2013)
Ethylene Emissions
14.0
Range of Measured Annual Averages
Median of Measured Annual Averages
Annual Average Measurements (ppb)
12.0
10.0
8.0
6.0
4.0
2.0
0.0
Year
Example (Cont.)
VOC Trends (BPA Area)
Annual Average Level of Propylene Measured in the BPA Area (1996-2013)
Propylene Emissions
10.0
Range of Measured Annual Averages
9.0
Annual Average Measurements (ppb)
Median of Measured Annual Averages
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
Year
Example (Cont.)
Source Characterization
• Photochemical
Modeling Project:
– 24 Natural Gas-fired
Refrigeration
Compressor Turbines
– 4 Acid Gas Vents
– 1 Marine Flare
– 2 Wet Gas Flares
– 2 Dry Gas Flares
– 2 Natural Gas-fired
Generator Turbines
– 2 Emergency
Generators
• Proposed Project:
– 6 Natural Gas-fired
Refrigeration
Compressor Turbines
– 1 LNG Storage LP Flare
– 1 Wet/Dry Gas Ground
Flare
– 1 Auxiliary Boiler
– 4 Thermal Oxidizers
– 7 Diesel Generators
– 1 Natural Gas-fired
Essential Generator
– 1 Blowdown Vent
Example (Cont.)
Source Characterization
Photochemical
Modeling
PTE NOx
Emissions
2,665.29 tpy
PSD Increment:
Proposed Project
PTE NOx
Emissions
681.46 tpy
PSD Increment:
Photochemical modeling approx. 4X more NOx than
proposed project.
Example (Cont.)
Meteorological Parameters and Regional Transport
BPA Area
Surface Pressure (HPA)
Relative Humidity (%)
Example (Cont.)
Meteorological Parameters and Regional Transport
BPA Area
Surface Roughness (m)
Temperature (oC)
Example (Cont.)
Meteorological Parameters and Regional Transport
BPA Area
Wind Vectors (knts)
Wind Velocity (knts)
Example (Cont.)
Model Results
Photochemical modeling results in the BPA Area
based on 4X as much NOx is between 0.1-0.5
ppb.
Questions?
Contact Information
Justin Cherry
–
(512) 239-0955
justin.cherry@tceq.texas.gov
Air Permits Division
Reece Parker
–
(512) 239-1348
reece.parker@tceq.texas.gov
Air Permits Division